Exercise capacity and natural frequency of occurrence and intensity is a reliable indicator of a person's mental and physical health status. A person of good physical and mental health will tend to regularly undertake physically taxing exertion either through dedicated exercise or through the course of their normal daily and recreational activities. The intensity and duration of the physical exertion is a good indicator of their overall physical health and the frequency with which it occurs is indicative of their mental health and attitude.
Conversely, a reduced level and/or capacity for exercise is correlated with a state of reduced mental and/or physical health. A state of depression, for example, is positively correlated with a reduced frequency and duration of physical exertion. A person suffering from depression will typically reduce the level of physical exertion they undertake to maintain a home, for example, and will typically exhibit a general lethargy and increased sedentary behavior. A person suffering from depression will also often avoid dedicated exercise.
A person suffering an acute or chronic physical impairment, such as a survivor of a myocardial infarction (MI) or a person with congestive heart failure (CHF) will typically have a reduced capacity for exercise. The limited cardio-vascular output of such persons limits the ability they have to engage in physically strenuous exercise. It is often the case that a person suffering a serious physical malady, such as MI or CHF, will also exhibit some depression symptoms further reducing their exercise level.
Thus, natural exercise frequency and intensity can be used as a general diagnostic for the physical and mental condition of a patient. Changes in the level and duration of exertion of which they are capable is also highly indicative of the progression of a condition, such as CHF, and is useful as an adjunct to other physiological measurements. It also provides valuable clinical feedback on the efficacy of treatment regimens.
FIG. 1 shows some general interactions and contributing factors to depression and some typical consequences thereof. Depression is often treated with tricyclic antidepressants. Common side-effects of the tricyclics is a decrease in heart rate variability and an orthostatic hypotension condition in the medicated patient. A decreased heart rate variability often leads to a decreased vagal tone which is an indicator for ventricular tachycardia/fibrillation (VTNF). As potentially lethal conditions, an increased risk of VT or VF leads to an increased mortality which typically causes increased anxiety in a patient aware of their condition. Increased anxiety tends to exacerbate depression thus forming a potential reinforcing cycle.
Depression also tends to lead to an exaggerated orthostatic response as well as decreased vagal tone and increased sympathetic tone. Decreased vagal tone and increased sympathetic tone also are indicators for increased VT and VF susceptibility, which as previously mentioned, leads to an increased mortality which can increase anxiety and the depressive condition and another potential reinforcement cycle.
As previously mentioned, depression tends to lead to a lower level of exercise and also a reduced compliance with following a medication regimen. Depression also tends to lead to an increase in aggragability of blood platelets. All three of these factors are risk factors for myocardial infarction. As previously mentioned, occurrence of an MI can lead to a CHF condition. CHF is also an indicator for increased mortality and another possible feedback path for a reinforced cycle of increased depression.
Thus, it can be understood that effectively treating a patient's depression and any underlying medical condition is important in securing the patient's overall health. Evaluating the patient's capacity for exercise can provide valuable information regarding the patient's current status and the effectiveness of treatment regimens. One widely used standard measure of a person's exercise capacity is a six-minute walk test. The six-minute walk test is generally performed on a stationary treadmill and measures the effective distance that a patient is able to walk in a six-minute period. The six-minute walk test is performed under standardized conditions and provides a repeatable, commonly accepted standard measurement tool.
A practical diagnostic drawback with this method of determining the patients condition is that it can require a stationary treadmill implement. This aspect is disadvantageous as it requires either installation of treadmill equipment at a patient's home for self-testing or a trip to a clinical setting equipped with a treadmill. The test can be administered as a true measure of actual distance traveled by walking, however this aspect introduces the difficulty of accurately determining the actual distance walked. Further, the six-minute walk test as typically administered is not a measure of the natural occurrence of a patient's exercise, but rather a measure taken under artificial conditions. Patient surveys can be administered to solicit information about their normal, natural activities, however, as is known in the art, self-surveys can be inaccurate particularly, if the patient is not performing exercise as requested by their physician.
Thus, it would be desirable to have a convenient, unobtrusive method of determining a patient's capacity for and natural frequency of taxing exercise. It would be advantageous to be able to gather the information in an invisible manner from the patient's perspective, e.g. without patient input or interaction, so as to reduce the patient's conscious awareness of the data gathering and thus reducing artificial impact on their natural tendencies. It would also be advantageous to gather information over an extended period of time so as to track the progression of a patient's condition over time. It would also be beneficial to automatically evaluate the patient's natural exercise activity in an equivalent to a clinical six-minute walk test to allow comparison to a standard measure.